It is common to utilize high density polyethylene (HDPE) piping to convey fluids in a wide spectrum of industries. Compared to more traditional steel pipe, HDPE pipe has a greater ease of installation, lower maintenance requirements and lower leakage rate making it a preferred conveyance medium in the water, energy and nuclear industries over its metallic alloy counterparts.
HDPE pipe sections are commonly joined together using a fusion process such as butt-fusion jointing. This process involves the simultaneous heating of adjacent ends of HDPE pipe sections to be joined until a molten state is attained on the contact surface of each end. The two surfaces are brought together under controlled pressure for a specific cooling time and a homogenous fusion joint is formed. Notwithstanding the foregoing, HDPE joints may have various flaws, such as lack of fusion, cold fusion (partial bond), inclusion (embedded foreign objects), and voids.
Current inspection techniques of HDPE pipe include visual inspection and phased array ultrasonic inspection. Phased array ultrasonic inspection is a technique which involves directing acoustical energy towards an object to determine whether the object contains flaws. HDPE material however, has some specific acoustic characteristics, such as hindering the propagation of shear sound waves, which make butt joint inspection utilizing phased array ultrasonic inspection difficult, particularly when the fusion line is perpendicular to the material surface as is the case with HDPE butt joints. Since the repair of a fused. HDPE pipe joint is typically expensive a need has arisen to optimally test the integrity of fused HDPE pipe joint in a non-destructive manner.